Class CachedMap
- All Implemented Interfaces:
Map
This class provides cache access to Map
collections.
Instance of this class can be used as "proxy" for any collection implementing the java.util.Map
interface.
Typically, CachedMap
are used to accelerate access to large collections when the access to the collection is
not evenly distributed (associative cache). The performance gain is about 50% for the fastest hash map collections
(e.g. FastMap
). For slower collections such as java.util.TreeMap
, non-resizable FastMap
(real-time) or database access, performance can be of several orders of magnitude.
Note: The keys used to access elements of a CachedMap
do not need to be immutable as they are not
stored in the cache (only keys specified by the put(java.lang.Object, java.lang.Object)
method are). In other words, access can be performed
using mutable keys as long as these keys can be compared for equality with the real map's keys (e.g. same
hashCode
values).
This implementation is not synchronized. Multiple threads accessing or modifying the collection must be synchronized externally.
This class is public domain (not copyrighted).
- Version:
- 5.3, October 30, 2003
- Author:
- Jean-Marie Dautelle
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Nested Class Summary
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionvoid
clear()
Removes all mappings from this map (optional operation).boolean
containsKey
(Object key) Indicates if this map contains a mapping for the specified key.boolean
containsValue
(Object value) Returnstrue
if this map maps one or more keys to the specified value.entrySet()
Returns an unmodifiable view of the mappings contained in this map.boolean
Compares the specified object with this map for equality.void
flush()
Flushes the key/value pairs being cached.Returns the value to which this map maps the specified key.Returns the backing map.int
Returns the actual cache size.int
hashCode()
Returns the hash code value for this map.boolean
isEmpty()
Returnstrue
if this map contains no key-value mappings.keySet()
Returns an unmodifiable view of the keys contained in this map.Associates the specified value with the specified key in this map.void
Copies all of the mappings from the specified map to this map (optional operation).Removes the mapping for this key from this map if it is present.int
size()
Returns the number of key-value mappings in this map.values()
Returns an unmodifiable view of the values contained in this map.Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
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Constructor Details
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CachedMap
public CachedMap()Creates a cached map backed by aFastMap
. The default cache size and map capacity is set to256
entries. -
CachedMap
public CachedMap(int cacheSize) Creates a cached map backed by aFastMap
and having the specified cache size.- Parameters:
cacheSize
- the cache size, the actual cache size is the first power of 2 greater or equal tocacheSize
. This is also the initial capacity of the backing map.
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CachedMap
Creates a cached map backed by the specified map and having the specified cache size. In order to maintain cache veracity, it is critical that all update to the backing map is accomplished through theCachedMap
instance; otherwiseflush()
has to be called.- Parameters:
cacheSize
- the cache size, the actual cache size is the first power of 2 greater or equal tocacheSize
.backingMap
- the backing map to be "wrapped" in a cached map.
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Method Details
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getCacheSize
public int getCacheSize()Returns the actual cache size.- Returns:
- the cache size (power of 2).
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getBackingMap
Returns the backing map. If the backing map is modified directly, thisCachedMap
has to be flushed.- Returns:
- the backing map.
- See Also:
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flush
public void flush()Flushes the key/value pairs being cached. This method should be called if the backing map is externally modified. -
get
Returns the value to which this map maps the specified key. First, the cache is being checked, then if the cache does not contains the specified key, the backing map is accessed and the key/value pair is stored in the cache.- Specified by:
get
in interfaceMap
- Parameters:
key
- the key whose associated value is to be returned.- Returns:
- the value to which this map maps the specified key, or
null
if the map contains no mapping for this key. - Throws:
ClassCastException
- if the key is of an inappropriate type for the backing map (optional).NullPointerException
- if the key isnull
.
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put
Associates the specified value with the specified key in this map.- Specified by:
put
in interfaceMap
- Parameters:
key
- the key with which the specified value is to be associated.value
- the value to be associated with the specified key.- Returns:
- the previous value associated with specified key, or
null
if there was no mapping for the key. - Throws:
UnsupportedOperationException
- if theput
operation is not supported by the backing map.ClassCastException
- if the class of the specified key or value prevents it from being stored in this map.IllegalArgumentException
- if some aspect of this key or value prevents it from being stored in this map.NullPointerException
- if the key isnull
.
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remove
Removes the mapping for this key from this map if it is present.- Specified by:
remove
in interfaceMap
- Parameters:
key
- key whose mapping is to be removed from the map.- Returns:
- previous value associated with specified key, or
null
if there was no mapping for key. - Throws:
ClassCastException
- if the key is of an inappropriate type for the backing map (optional).NullPointerException
- if the key isnull
.UnsupportedOperationException
- if theremove
method is not supported by the backing map.
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containsKey
Indicates if this map contains a mapping for the specified key.- Specified by:
containsKey
in interfaceMap
- Parameters:
key
- the key whose presence in this map is to be tested.- Returns:
true
if this map contains a mapping for the specified key;false
otherwise.
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size
public int size()Returns the number of key-value mappings in this map. If the map contains more thanInteger.MAX_VALUE
elements, returnsInteger.MAX_VALUE
. -
isEmpty
public boolean isEmpty()Returnstrue
if this map contains no key-value mappings. -
containsValue
Returnstrue
if this map maps one or more keys to the specified value.- Specified by:
containsValue
in interfaceMap
- Parameters:
value
- value whose presence in this map is to be tested.- Returns:
true
if this map maps one or more keys to the specified value.- Throws:
ClassCastException
- if the value is of an inappropriate type for the backing map (optional).NullPointerException
- if the value isnull
and the backing map does not not permitnull
values.
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putAll
Copies all of the mappings from the specified map to this map (optional operation). This method automatically flushes the cache.- Specified by:
putAll
in interfaceMap
- Parameters:
map
- the mappings to be stored in this map.- Throws:
UnsupportedOperationException
- if theputAll
method is not supported by the backing map.ClassCastException
- if the class of a key or value in the specified map prevents it from being stored in this map.IllegalArgumentException
- some aspect of a key or value in the specified map prevents it from being stored in this map.NullPointerException
- the specified map isnull
, or if the backing map does not permitnull
keys or values, and the specified map containsnull
keys or values.
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clear
public void clear()Removes all mappings from this map (optional operation). This method automatically flushes the cache.- Specified by:
clear
in interfaceMap
- Throws:
UnsupportedOperationException
- if clear is not supported by the backing map.
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keySet
Returns an unmodifiable view of the keys contained in this map. -
values
Returns an unmodifiable view of the values contained in this map. -
entrySet
Returns an unmodifiable view of the mappings contained in this map. Each element in the returned set is aMap.Entry
. -
equals
Compares the specified object with this map for equality. Returnstrue
if the given object is also a map and the two Maps represent the same mappings. -
hashCode
public int hashCode()Returns the hash code value for this map.
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